The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Matrix acidizing of sandstone reservoirs has been carried out for years in order to increase production of oil or gas from hydrocarbon bearing reservoirs or to improve the injectivity of reservoirs undergoing water-injection. The most common main treatment fluids used to dissolve clays and other aluminosilicate minerals are “mud acid” formulations, which are essentially strongly acidic solutions that contain hydrofluoric acid (HF). A key to sandstone matrix stimulation is to maximize the dissolution of damaging aluminosilicate particles (that line and clog the pore space) while minimizing precipitation reactions during the main treatment stage of fluid. Minimizing precipitation limits the potential for damage to the overall formation productivity. This interplay between the favorable dissolution-kinetics and the kinetics of unfavorable secondary precipitation reactions has fueled research meant to gain a better understanding and control of the reaction kinetics of dissolution. In particular, at high temperatures the dissolution reactions in a sandstone matrix are so fast that the resulting precipitation reactions are often uncontrollable.
For many years, organic acids and organic chelating agents have been added to matrix acidizing fluids to minimize precipitation by chelating the metal cations generated in solution. Many of these chelating agents have included such organic acids/chelants as ethylenediaminetertaacetate (EDTA), 2-hydroxyethylethylenediaminetriacetate (HEDTA), nitrilotriacetate (NTA), diethylenetriaminepentaacetate (DTPA), and citric acid, for example. The literature shows that these compound's association constants toward common oilfield metal cations, such as iron, calcium, magnesium, aluminum, and many others, are very strong and minimize the secondary precipitation of their reaction byproducts.
Currently, one of the most dramatic reasons for failure of sandstone matrix acidizing treatments to realize their full stimulation potential is the precipitation of amorphous silica. Unfortunately, the above-mentioned organic chelating agents demonstrate limited ability to either chelate silicon cations/silicate particles or to prevent the precipitation of amorphous silica. Previous attempts at preventing the precipitation of such amorphous silica have shown limited success.
Accordingly, a need exists for new treatment methods and fluids for treating sandstone subterranean formations in oil and gas producer wells and water-injector wells that can minimize the precipitation of amorphous silica during sandstone acidizing treatments toward optimized stimulation of productivity of the formation.